JP2004506306A - Switching device - Google Patents

Abstract

The switching device operates the high-pressure discharge lamp at a voltage having successive periods of opposite polarity. The switching device has an input terminal for connecting a power supply, an output terminal for connecting the lamp to be operated, a control means for controlling a switch mode power supply and the switch mode power supply, and a voltage across the lamp. Means for forming a corresponding ramp signal. According to the invention, the switching device comprises means for detecting a DC current through the high-pressure discharge lamp and / or a DC voltage across the high-pressure discharge lamp.

Description

が最後の４つの結果Ｕｌｎ乃至Ｕｌ（ｎ−４）から算出され、ＵｌｎとＵｌ（ｎ−１）との間の電圧における差が算出される。次いで、比較手段は、電圧における差Ｕｖが平均電圧
【数２】

のある割合（ｆｒａｃｔｉｏｎ）ｆ、例えば５０％を超えるかどうかを決定するために比較ＣＩを行う。超える場合には、度数計Ｔが１だけ増やされる。次いで、次の比較ＣＩＩにおいては、度数計のコンテンツが制限値Ｇに達しているかどうかが決定される。達している場合には、スイッチモード電源がスタンバイモードＳＢＭに切り換えられる。達していない場合には、後続の電圧検出が行われる。比較ＣＩが、Ｕｖが平均電圧
【数３】

の前記割合ｆ以下であることを明らかにする場合には、度数計Ｔのコンテンツが１だけ減らされ、後続の電圧検出が行われる。
【００２１】
本明細書に記載の例は、投影システム、とりわけライトバルブプロジェクタ（ｌｉｇｈｔ ｖａｌｖｅ ｐｒｏｊｅｃｔｏｒ）の一部を形成する。
【図面の簡単な説明】
【図１】本発明によるスイッチング装置を概略的に示す。
【図２】公称動作時の電圧の電圧図を示す。
【図３】直流電流動作時の電圧の電圧図を示す。
【図４】図１によるスイッチング装置において用いられるアルゴリズムを概略的に示す。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is a switching device for operating a high-pressure discharge lamp at a voltage having a period of continuous opposite polarity,
An input terminal for connecting the power supply;
-An output terminal connecting said lamp to be operated;
-A switch mode power supply and control means for controlling the switch mode power supply;
Means for forming a ramp signal corresponding to the voltage across said lamp.
[0002]
The invention also relates to a projection apparatus having a switching device which can suitably be used for operating a high-pressure discharge lamp.
[0003]
[Prior art]
A switching device of the type described in the opening paragraph is known from International Patent Application Publication No. WO 00/36882 (Applicant's serial number: D98161). This known switching device controls the power supplied to the lamp by the microprocessor such that the shape of the current through the lamp can be adjusted for each period of the supply voltage having successive periods of opposite polarity. Means for enabling The shape of the current flowing through the lamp is adjusted based on the lamp signal corresponding to the voltage across the lamp. In this manner, lamp flicker and unstable burning can be significantly reduced. Known switching devices can be suitably used, inter alia, to operate high-pressure discharge lamps in projection systems, such as projection television receivers.
[0004]
[Problems to be solved by the invention]
However, a disadvantage of the known switching device is that it is very complex and furthermore offers protection against lamp damage, for example as a result of asymmetric operation of the lamp over a long period of time. It is not provided.
[0005]
[Means for Solving the Problems]
It is an object of the present invention to provide means for overcoming the disadvantages. This is achieved in accordance with the invention by a switching device of the type described in the opening paragraph, characterized in that the switching device comprises means for detecting a DC current through the high-pressure discharge lamp or a DC voltage across the high-pressure discharge lamp. Achieved.
[0006]
An advantage of the switching device according to the invention is that unwanted long-term asymmetries in the operation of the lamp can be detected in a relatively simple manner. The asymmetric operation of the lamp is based on the fact that the lamp effectively carries a DC voltage and / or DC current for a length of time spanning at least two successive periods of opposite polarity. The detection of the direct current through the high-pressure discharge lamp or of the direct-current voltage across the high-pressure discharge lamp is preferably performed by means of a lamp signal. This has the advantage that the complexity of the switching device is still limited.
[0007]
In an advantageous embodiment of the switching device according to the invention, the formation of the ramp signal relates to a time-sequential voltage detection, the means for performing said detection comprising a comparison means for comparing successive voltage detections. . In this manner, the voltage difference between successive voltage detections can be advantageously determined.
[0008]
Preferably, the switching device comprises a commutator and a ramp signal is formed between the output of the switch mode power supply and the commutator. This has the important advantage that improper functioning of the commutator is also detected. Improper operation of the commutator, generally as a result of improper switching of one of the commutator switches, is a significant factor in the DC current or DC voltage operation of the lamp. The possibility of monitoring the proper operation of said commutator by means of heat detection is very complicated, given the fact that the commutator in the switching circuit of a high-pressure discharge lamp often has four switching elements. It is difficult to implement because it requires at least two, and preferably four, heat detection circuits that will result in the procedure.
[0009]
In an advantageous embodiment of the switching device, the detection means comprises, after each voltage detection, a counter which is held based on the result of the comparison between the determined voltage difference and the average voltage, at which a threshold is exceeded. And may be suitably used to implement an algorithm in which a control signal for switching the switch mode power supply to the standby mode is generated.
[0010]
Surprisingly, for continuous voltage detection, it has been found that voltage detection during each of the successive periods of opposite polarity is sufficient. As a result, the switching device remains relatively simple. If the lamp signal to be detected contains a relatively large amount of noise, it may be advantageous to use a filter circuit in the switching device, for example in the form of an analog low-pass filter. Another possible filter technique is, for example, a digital filter technique that averages two or more voltage detections during each of the successive opposite polarity periods.
[0011]
Preferably, the average voltage is formed from a moving average of the voltage detection during the last four consecutive opposite polarity periods. This has the important advantage that the average voltage used as reference value is associated with the individual lamp. As a result, the difference in characteristics between the individual lamps has no significant effect on the reliable operation of the switching device.
[0012]
Experiments have shown that if the determined voltage difference exceeds 50% of the average voltage, this voltage difference can be used as a measure of the DC current through the lamp or the generation of a DC voltage across the lamp. Was. In such a case, increasing the frequency meter by one makes it possible to monitor the frequency of the DC current flowing through the lamp or the DC voltage applied to both ends of the lamp. Preferably, if the determined voltage difference is less than or equal to 50% of the average voltage, the frequency meter is reduced by one. In this way, the effects of accidental fluctuations in the current through the lamp or the voltage across the lamp are largely eliminated in a simple and reliable manner.
[0013]
These and other features of the present invention will be described and elucidated with reference to the embodiments described hereinafter.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows a switching device suitable for operating a high-pressure discharge lamp at voltages having successive periods of opposite polarity, in which K1 and K2 are input terminals connecting a power supply. Yes, L1 and L2 are output terminals for connecting the high-pressure discharge lamp LA to be operated. I represents a switch mode power supply, II represents a commutator, and III represents control means for controlling the switch mode power supply and the commutator. The switching device further comprises means VD for forming a ramp signal corresponding to the voltage across the lamp. The switching device also comprises means DCM for detecting a direct current through the high-pressure discharge lamp or a direct-current voltage across the high-pressure discharge lamp.
[0015]
The means VD for forming the ramp signal is connected to a connection point L3 between the output of the switch mode power supply and the commutator. As a result, the ramp signal is formed as a voltage detection at the output of the switch mode power supply.
[0016]
In a practical embodiment of the switching device according to the above example, this switching device can be suitably used to operate a Philips UHP132W type lamp. The commutator has four MOSFET switches that are periodically turned on and off by two. In the above example, switching of the commutator switch is performed at a fixed frequency, for example, 90 Hz. In another example, the commutator switching is synchronized with the video signal from the projection system by a control signal. The switch-mode power supply is a buck converter or (step) down-converter comprising switching elements which are turned on and off at high frequency by control means, for example a control signal generated by PWM. A boost converter or (step) up converter may precede a buck converter or (step) down converter. A resistive voltage divider connected to node L3 forms part of means VD for forming a ramp signal corresponding to the voltage across the lamp. Part of the means VD for forming the ramp signal as a time-sequential voltage detection of the voltage at the tap on the resistor divider forms part of a Philips 83747 type programmable IC 80C51. The programmable IC with the following algorithm also forms a means DCM for detecting the direct current through the high-pressure discharge lamp or the direct-current voltage across the high-pressure discharge lamp. This IC also forms part of the control means III. The means DCM serves to periodically compare successive voltage detections.
[0017]
For the frequency meter, use is made of a RAM memory housed in the IC. In a practical example, the switch mode power supply is switched to the standby mode as soon as the meter reaches 750. In the standby mode of the switch mode power supply, the control means ensures that the voltage at the output of the switch mode power supply is so low that discharge cannot be sustained in the lamp.
[0018]
In FIGS. 2 and 3, time is plotted along the horizontal axis, and voltage is plotted along the vertical axis. In the voltage diagram shown in FIG. 2, VL1 shows the change in the voltage across the connecting lamp when no asymmetric operation of the lamp is performed. At time points t1, t2, t3, t4 and t5, commutation of the commutator that causes the voltage to have a continuous period of opposite polarity is performed. Thus, the period between t1 and t2 and the period between t3 and t4 form a period having a positive polarity, while the period between t2 and t3 and the period between t4 and t5. The period is a period of negative polarity. The periodic voltage detection by means VD results in the formation of a ramp signal with a change according to S1.
[0019]
In FIG. 3 as well, VL2 forms a voltage change across the connecting lamp when asymmetrical operation of the lamp takes place, in which case a direct current flows through said lamp or a direct current voltage Is applied to both ends of the lamp. In this case, the shape of the ramp signal for voltage detection corresponds to S2.
[0020]
The algorithm provided by the example programmable IC described herein is schematically illustrated in FIG. After igniting the lamp and reaching a stable combustion state, indicated by START, a voltage detection is performed at time tn, the result of which is indicated by Uln. Then, the average voltage

Is calculated from the last four results Uln to Ul (n-4), and the difference in voltage between Uln and Ul (n-1) is calculated. Then, the comparing means determines that the difference Uv in the voltage is the average voltage

A comparison CI is performed to determine if the ratio exceeds a certain fraction f, eg, 50%. If so, the frequency counter T is incremented by one. Then, in the next comparison CII, it is determined whether or not the content of the frequency counter has reached the limit value G. If so, the switch mode power supply is switched to the standby mode SBM. If not, subsequent voltage detection is performed. The comparison CI indicates that Uv is the average voltage.

Is determined to be equal to or less than the above-mentioned ratio f, the content of the frequency counter T is reduced by 1 and the subsequent voltage detection is performed.
[0021]
The examples described herein form part of a projection system, in particular a light valve projector.
[Brief description of the drawings]
FIG. 1 shows schematically a switching device according to the invention.
FIG. 2 shows a voltage diagram of a voltage in a nominal operation.
FIG. 3 shows a voltage diagram of a voltage during DC current operation.
FIG. 4 schematically shows an algorithm used in the switching device according to FIG. 1;

Claims (11)

A switching device for operating a high pressure discharge lamp at a voltage having a period of continuous opposite polarity,
An input terminal for connecting the power supply;
-An output terminal connecting said lamp to be operated;
-A switch mode power supply and control means for controlling the switch mode power supply;
Means for forming a lamp signal corresponding to the voltage across the lamp, comprising means for detecting a DC current through the high-pressure discharge lamp or a DC voltage across the high-pressure discharge lamp. A switching device characterized by the above-mentioned. The switching device according to claim 1, wherein detection of a DC current through the high-pressure discharge lamp or a DC voltage across the high-pressure discharge lamp is performed by the lamp signal. 2. The switching device according to claim 1, wherein the formation of the ramp signal relates to time-series voltage detection, and the means for performing the detection includes a comparing means for comparing continuous voltage detection. 4. The switching device according to claim 3, wherein the comparing means is adapted to determine a voltage difference between the successive voltage detections. 3. The switching device according to claim 2, wherein the switching device comprises a commutator, and wherein the ramp signal is formed between an output of the switch mode power supply and the commutator. The detection means, after each voltage detection, a frequency meter is held based on the result of the comparison between the determined voltage difference and the average voltage. 5. The switching device according to claim 4, wherein the switching device can be suitably used to execute an algorithm that generates a control signal for switching to a standby mode. 4. The switching device according to claim 3, wherein the continuous voltage detection is performed by voltage detection in each of the successive periods of the opposite polarity. 7. The switching device according to claim 6, wherein the average voltage is formed from a moving average of voltage detection during the last four consecutive periods of opposite polarity. 9. The switching device according to claim 6, wherein the frequency meter is increased by one when the determined voltage difference exceeds 50% of the average voltage. 9. The switching device according to claim 6, wherein the frequency meter is reduced by one when the determined voltage difference is equal to or less than 50% of the average voltage. A projection device comprising a switching device according to any of the preceding claims, which can be suitably used for operating a high-pressure discharge lamp.